Potentiometric devices



Nov. 11, 1958 I B. F. HUBBARD ETAL 2,

POTENTIOMETRIC DEVICES Filed Feb. 5, 195a Bwem/v fifflusawea INVENTORs.

United States Patent POTENTIGMETRIC DEVICES Burton F. Hubbard and Gaynard H. Fosdick, Pomona, Calif.

Application February 3, 1956, Serial No. 563,272

Claims. (Cl. 201-62) This invention relates generally to potentiometry; more particularly it relates to a compact and economically manufactured device for accurately controlling or measuring potential and potential ratios under adverse environmental conditions. While potentiometers and variable resistors have been long known and utilized in differing combinations with other electrical devices and circuits, continuing progress in the electronic arts has given rise to a demand for potentiometric devices fulfilling various stringent requirements. This demand is particularly great in fields in which the devices are unavoidably subjected to adverse environmental conditions, such as severe shock and vibration. Such conditions generally result in distortion of the information conveyed or transmitted by the potentiometric apparatus involved, or in damage and in malfunctioning or failure or" the devices. The consequences of in accuracy or failure in telemetering, aviation or other applications in which certainty and accuracy of information control or transmission are important are very serious, as is well known in the art.

It is, therefore, a primary object of our invention to provide a potentiometric device of compact size, which can be manufactured economically by mass production methods; which is relatively free from shock and vibrational distortion; which is free, in its brush construction, from contact bounce, and which has a high selectivity of measured or controlled potential, easily obtained and accurately maintained.

A more specific object of our invention is to furnish a potentiometric device in which a dielectric contact retaining member, or travel block, is securely retained against transverse and rotational movement by a pair of shoulders which abut slide surfaces on a conductor and resistance support block and by a U-shaped cover member. The retention of the travel block of our device on'all four of its sides by the support block and the sides and top of the cover are important aspects of our invention because theyshelp insure freedom from vibrational distortion and loss of position of the contact brush along the resistance element.

It is an object of our invention to provide a potentiometric device having a high natural frequency contact brush secured to a dielectric travel block reciprocable linearly by a threaded lead screw upon a support block within a retaining casing.

Another object of our invention is to provide a potentiometric device in which a selected contact position of the brush can be accurately, positively and easily obtained by rotation of a lead screw which engages a brush retaining travel block. 7 v 7 Another object of our invention is the provision of an improved brush construction for potentiometers such that contact bounce is substantially eliminated while contact resistance is maintained at the lowest practical level.

A further object of our invention is to provide a potentiometric device which is fully enclosed and protected See from the introduction of dust and fumes while accurate adjustment of brush contact position is permitted.

Other objects and features of the present invention, as well as many advantages of it, will be apparent to those skilled in the art from a consideration of the remainder of this description, the appended claims, and the accompanying drawings in which:

Figure 1 is a perspective view of a potentiometric device according to the present invention;

Figure 2 is a longitudinal sectional view taken at line 2-2 of Figure 1;

Figure 3 is a transverse sectional view taken at line 33 of Figure 2; and

Figure 4 is an exploded view illustrating the basic elements of our device.

In all figures of the drawings like numerals are used to designate like parts for convenience of explanation.

Referring to the drawings and more particularly to Figures 2, 3 and 4, there is illustrated a preferred embodiment of the potentiometric device of the present invention. This device is a rectilinear potentiometer. The casing is composed of a male base member 1, which is U-shaped in longitudinal section, and a female cover member 2, which is U-shaped in transverse section. These elements are constructed of any suitable material such as aluminum. Base member 1 is of the same width as the internal width of cover member 2. The mating surfaces of these members are precision machined or otherwise precision formed in order to provide a close tolerance fit. Thus when the base and cover members are secured to one another as by screws 3, an integral casing is formed which has maximum rigidity in all stress planes and therefore provides maximum vibrational and environmental protection.

Support block 4, which is substantially the same length and width as the internal length and width of the base member 1, is secured thereto by screw 5. The ends of block 4 mate with the internal surfaces of the end uprights 6 of U-shaped base 1 and the sides of block 4 are adapted to mate with the internal side surfaces of cover member 2, thus rendering the support block an integral unit with the casing. Block 4 is constructed of suitable dielectric material, such as nylon or polystyrene, and is provided in its rectangular face with a slot 7 and a rectangular recess 8, both of which extend longitudinally of the block in parallel spaced relationship. Rectangular cut-out sections 9 extend transversely along opposite ends from the internal surface defining an extension of the interior side of recess 8 in order to form receiving surfaces 10 for screw terminals 11 and 12.

Resistance element 13, which is constructed of a l1ol low glass mandrel upon which a coil of fine resistance wire is wound, is cemented or otherwise securely positioned Within recess 8. The end wires of this element are fastened to their adjacent terminals 11 and 12. A conductor bar 14, of suitable electrical contact material and rectangular in cross section, is fitted Within slot 7 and fixedly retained therein as by cementing.

Lead wires 15, 16 and 17 are introduced into the easing through precision machined holes 18, which are provided in one of the end uprights 6 of base member 1. These holes have diameters corresponding with the diameters of the lead wires thereby providing a close tolerance fit and assuring an effective seal between the interior and exterior of the casing. Lead wire 15 is electrically connected to one end of conductor bar 14 at terminal 19 while lead wire 16 is inserted through hollow resistance element 13 and soldered to terminal 12. Lead wire 17 is soldered to the most nearly adjacent terminal 11. It will be evident that our construction completely avoids the necessity for bending lead wires along specially provided passageways and renders the base assembly comprising base member 1, support block 4, resistance element 13, conductor bar 14 and the lead wires an integral unit, which is easily and economically manufactured.

It will be noted that the face of block 4 has longitudinally extending shoulders 29 and 21 exteriorly of slot 7 and recess 8. These shoulders have parallel, flat, smooth surfaces upon which a contact carrying element or travel block 22 is slidably supported and adapted to ride. This structure is extremely important to the accomplishment of our objectives since such abutment of shoulders 20 and 21 of the dielectric block, in which are mounted resistance element 13 and conductor bar 14, with mating surfaces of contact brush retaining travelblock 22 obviously results in a fixed uniform contact relation between the contact brush on one hand and resistance element 3 and conductor bar 14 on the other hand, while permitting changes in the longitudinal position of contact therebetween. As shown in Figures 3 and 4, shoulder 21 is milled down below the surface plane of shoulder 20 in order to provide a greater surface of contact with the side surface of cover member 2 for travel block 22 which, upon assembly, rides upon shoulders 20 and 21 of support block 4.,

Travel block; 22 is U-shaped in transverse section to provide a channel or recess 23 for receiving a contact brush 24 and is L-shaped in longitudinal section in order to provide a sufficiently wide surface to facilitate the mounting of brush retaining screws 25 which secure the brush in position within the recess.

With further reference to the specific structure of our device, travel block 22 is provided with a longitudinally extending threaded hole 26, threaded to receive a leadscrew 27. The latter element is journaled at its end and has a journaled neck 28, intermediate of a threaded shank 29 and a slotted head 30. Upon assembly leadscrew 27 is inserted through bearing hole 31 in one of the uprights 6 of base member 1, screwed through the travel block and inserted into a bearing recess 32 provided in the other upright of the base member. The lead-screw is retained against linear displacement by an E retainer 33 receivable by an annular groove in its shank and by peripheral shoulder 34 of the head. Cover member 2 is fitted over the base assembly and travel block and secured to the base member to form the completed device. The internal dimensions of the casing correspond with the width of both the travel block and the support block and with the total combined depth of these elements. Upon activating travel block 22 linearly by means of lead screw 27 to alter the longitudinal contact position of the brush it will be apparent that it is supported against all undesired rotational and translational displacement through the coaction with it of shoulders 29 and 21 and the inner surfaces of cover member 2. A travel block constructed of material having an ability to provide its own lubrication and having a low coefiicient of friction, such as. nylon, obviously gives improved results since such an element, though well supported, is nevertheless easily activated.

It has been found in practice that greatly improved operative results are obtainable if the material used in the construction of travel block 22 possesses a specific combination of physical and chemical properties. The material must first have a good dielectric characteristic. It

must have and retain rigidity over a reasonable temperature range. It should possess a low coelficient of friction and have the additional property of self-lubrication. It is important that it possess resiliency and high elastic recovery.- The improved results to be obtained through utilization of the latter properties will become apparent from the consideration hereinbelow of the travel block and lead screw combination. It has beenfound in practice that nylon is. a very suitable construction material for brush-retaining travel block 22.. I s

We have; discovered that linear position retention of block 22 is attainable, even in the face of extreme w'bration and of shock inherent in certain environmental con- ,ditions of use, by precision threading longitudinally extending hole 26 in such manner that when the male screwthreads of lead screw 27 are fitted into the female screwthreads in travel block 22, the latter threads are elastically deformed. An example of a method of accomplishing this would be to establish the depth of the threads in travel block 22 at a depth less than that of the threads on screw thread27, by providing a flat portion dividing adjacent threads. Another example would be to provide a larger thread angle for the threads in travel block 22 than for the threads on lead screw 27. The elastic deformation, together with the use of a material of high elastic recovery for travel block 22 assures good position retention despite adverse environmental conditions -be cause the thread surfaces of the travel block effectively grip those of lead screw 27. The torsional force which must be applied to lead screw 27 is measurably greater at the commencement of rotation than upon continued rotation. This facilitates fine or Vernier adjustment of travel block position.

The use of resilient material of high elastic recovery for travel block 22 makes it possible to provide a gripping action on brush-retaining screws 25 like the gripping action of the travel block on lead screw 27. This insures against loosening or shifting of brush 24 with re: spect to travel block 22 under adverse environmental conditions. V

The use of material having a low coeificient of friction, such as nylon, for travel block 22 insures ease of movement of the block by rotation of lead screw 27. Friction between its threads and those of lead screw 27 is reduced. Friction between the surfaces of travel block 22 and the inner surfaces of cover member 2 is also reduced.

A further important aspect of our invention resides in the construction of contact brush 24. This brush is made of thin, spring, platinum alloy sheet and has a rectangular strip 36 provided with a pair of holes 37 for receipt of retaining screws 26. Extending perpendicularly from an edge of this strip are a pair of spaced parallel V-shaped contact elements 38 having accurate contact portions 39 at their terminal ends. We have found that this structure provides a contact brush having a high natural frequency, efl ectively diminishing contact bounce.

The applications in which our device may beutilized will be evident to those skilled in the art and need not be specifically enumerated. However, an example of a use to which our device is well adapted is as a component in the telemetric reception or transmission of information. Circuitry in this field requires potentiometric devices that measure or adjust ratios of voltages across certain portions of the circuits while assuring maintenance of contact position of the element under stress. The ratio of voltages across terminals 11 and 19 and across terminals 12 and 19 may be accurately and easily obtained by varyingthe position of contact of brush 25 on resistance element 13 by rotation of lead-screw 27.

Although a specific embodiment of the invention has been described and illustrated-in detail, it is to be clearly understood that the same is by way of illustration and example only; it is to be understood that the invention is not limited thereto, as many variations will be readily apparent to those versed in the art and. the inyeution is to be given'its broadest possible interpretation within" the terms of the following claims:

We claim: I

1. A potentiometric device comprising a casing having a support block, a resistance element and a conductor bar in parallel spaced relationship and fixed to said support block, a travel block having means directly slidable upon 'said support block, a contact element secured to said travel block and slidably engaging said resistanceelement and said conductor bar,=and'means engaging'saidtravel block: for imparting; linear niotiontheret a 2. A potentiometric device comprising a casing, a dielectric support block secured thereto, a resistance element and a conductor bar fixed to said support block, a travel block having extending portions directly slidable upon said support block, said travel block slidably contacting the cover surface and side surfaces of said casing, a brush secured to said travel block slidably contacting said conductor bar and said resistance element, and means engaging said travel block for imparting linear motion thereto. a

3. A potentiometric device comprising a casing, a support block secured thereto, a resistance element and a conductor bar in parallel spaced relationship and fixed to said support block, a travel block slidably mounted upon said support block, a contact brush secured to said travel block and slidably engaging said resistance element and said conductor bar, and a lead-screw threadedly engaging said travel block, said lead-screw being rotatably mounted upon said casing and being retained against linear displacement.

4. The potentiometric device of claim 3 wherein said travel block slidably engages the cover surface and side surfaces of said casing.

5. The potentiometric device of claim 4 wherein said travel block is constructed of resilient material having high elastic recovery, the threads of said travel block being so constructed and arranged that they undergo elastic deformation upon engaging the threads of said lead-screw.

6. The potentiometric device of claim 4 wherein said travel block is constructed of nylon, the threads of said travel block being so constructed and arranged that they undergo elastic deformation upon engaging the threads of said lead-screw.

7. A potentiometric device comprising a body member, a resistance element and a conductor bar in parallel spaced relationship-and secured to said body member, said body member having a pair of parallel shoulders exteriorly disposed with respect to said conductor bar and said resistance element, a travel block having secured thereto a contact brush in sliding contact with said conductor bar and said resistance element and said travel block having a pair of shoulders slidably retained against said body member shoulders, and means responsive to a torsional force for sliding said block upon said body member.

8. The potentiometric device of claim 7 in which said contact brush comprises a flat rectangular strip and a pair of spaced parallel V-shaped contact elements extending perpendicularly therefrom and having arcuate contact portions at their terminal ends.

9. A potentiometric device comprising a casing, a dielectric support block retained therewithin, a conductor bar and a resistance element secured to the support block, a lead-screw rotatably mounted within said casing and secured against longitudinal and lateral displacement, a travel block slidably supported upon said support block, said travel block having a threaded hole engaging said lead-screw for linear extension of said block thereupon, and a contact brush secured to said travel block in sliding contact with said conductor bar and said resistance element.

10. A potentiometric device comprising a heavy U-shaped base member, a dielectric support block secured thereto, said block having a rectangular recess and a longitudinal slot interiorly of a pair of longitudinal slide shoulders, a resistance element secured within said recess, a conductor bar secured within said slot, a dielectric travel block recessed interiorly of a pair of slide shoulders and having a threaded longitudinally extending hole, said slide shoulders of said travel block abutting said slide shoulders of said support block, a contact brush retained within said interior recess of said travel block, said brush being in contact with said resistance element and said conductor bar, a lead-screw rotatably mounted and secured against longitudinal displacement within bearing holes provided in the uprights of said base member, said lead-screw being threaded through said longitudinally extending hole of said travel block, and a U-shaped cover member mating with and secured to said base member.

11. The potentiometric device of claim 10 wherein said dielectric travel block is constructed of nylon.

12. A potentiometric device comprising a casing, a support block mounted therewithin, a resistance element and a conductor bar in parallel spaced relationship and fixed to said support block, said support block having a pair of parallel shoulders, one on either side of said resistance element and said conductor bar, a travel block having a pair of parallel spaced shoulders slidably engaging said support block shoulders, said travel block having a recess intermediately of said shoulders, a contact brush in sliding contact with said conductor bar and said resistance element, said brush being fixed to said travel block and disposed within said recess, and a lead-screw rotatably mounted and secured against linear displacement in said housing in parallel relationship with said conductor bar and resistance element, said leadscrew having said travel block threaded thereon.

13. The potentiometric device of claim 12 wherein said travel block slidably abuts the cover surface and side surfaces of said casing.

14. The potentiometric device of claim 12 wherein said resistance element comprises a resistance wire coil wound upon a non-conductive core having a longitudinal bore to accommodate a lead wire extending therethrough.

15. The potentiometric device of claim 12 wherein said travel block is constructed of resilient material having high elastic recovery, the threads of said travel block being so constructed and arranged that they undergo elastic deformation upon engaging the threads of said lead-screw.

16. The potentiometric device of claim 15 wherein said travel block is constructed of nylon.

17. The potentiometric device of claim 12 wherein screws secure said brush to said travel block, said travel block being constructed of resilient material having high elastic recovery and undergoing elastic deformation upon engaging said screws.

18. The potentiometric device of claim 17 wherein said travel block is constructed of nylon.

19. A potentiometric device comprising a heavy U- shaped base member rectangular in plan view, a support block secured to said base member and having its ends abutting the uprights of said base member, a hollow coil resistance element and a conductor bar secured in parallel spaced relationship to said base member interiorly of a pair of shoulders extending longitudinally of said base member, a travel block having a pair of shoulders exteriorly of a recess provided in said travel block, said shoulders being in sliding contact with said base member shoulders, a contact brush secured to said travel block within said recess of said travel block, said contact brush being in sliding contact with said conductor bar and said resistance element, a lead screw rotatably mounted and secured against linear displacement in said uprights parallel to said shoulders, said travel block being threadedly engaged by said lead-screw, a plurality of lead wires extending through openings provided in one of said uprights, the first of said wires being secured to end of said conductor bar, the second of said wires being connected to a terminal adjacent said upright and the third of said wires extending through said hollow coil and being secured to a terminal adjacent the opposite upright, and a U-shaped cover member mating with said member and secured thereto.

20. A potentiometric device comprising a casing, a support block secured thereto, a resistance element and a conductor bar in parallel spaced relationship and fixed to said support block, a travel block, a contact brush secured. to. said travel block and slid'ably engaging said.

resistance element and said conductor bar, a lead screw rotatably mounted within said, casing, said travel. block having a threaded hole adapted to receive and cooperate with said lead screw and being constructed of material having high elastic recovery, the threads of said lead screw having a configuration different from the configuration of the threads in said hole to cause elastic deformation of said travel block.

I References Cited in the fileof this patent UNITED STATES PATENTS 1,909,136" Thomas May 16, 1933 8 Rubinstein May 20, Batcheller Dec. 22, Jones Dec. 21, McLoughlin et a1 Oct. 10, Benander Nov. 12, Cooper Nov. 22, Searle Feb. 2,, Riley Aug. 24, Bourns et al Apr. 12, Bourns Jan. 15, Bourns; et a1. July 16,

FOREIGN PATENTS Great Britain July 10, 

